Auto-Cascade Refrigeration Layout for Stable Low-Temperature Cooling
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Solution Overview
Problem
Auto-cascade refrigeration systems face challenges in achieving efficient low temperatures and stability, particularly in smaller scales due to the complexity of plate heat exchangers and issues with overloading, which limits their application in cryogenic refrigeration despite their efficiency on a larger scale.
Innovation Solution
The system incorporates a sub-cooler acting as both a heat exchanger and liquid reservoir, with a phase separator and flow metering devices that create a Venturi effect to enhance heat transfer and stability, using refrigerants like HFC-32 and ethane to maintain efficient operation across different modes, and incorporates a swan neck configuration to prevent oil contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If plate heat exchangers are used in auto-cascade refrigeration systems, then heat transfer efficiency is improved, but device complexity and difficulty of optimization increase
Solution Approach 1:
The patent combines multiple heat exchangers into a compact integrated assembly where condensate from one heat exchanger flows directly to another in series. This merging approach maintains the high heat transfer efficiency of plate heat exchangers while reducing overall system complexity and optimizing space utilization.
Solution Approach 2:
The heat exchanger system is segmented into multiple stages with distinct functions - condensation stages followed by evaporation stages - allowing each segment to be optimized independently while working together as an integrated system, thereby managing complexity through functional decomposition.
2Productivity
If plate heat exchangers are used to achieve low temperatures, then refrigeration efficiency is improved, but tolerance to overloading conditions decreases
Solution Approach 1:
The system incorporates a liquid reservoir positioned to receive excess condensate from the heat exchangers before it can cause overloading conditions. This reservoir acts as a buffer that cushions against sudden heat loads or overloading conditions, maintaining system reliability while preserving refrigeration efficiency.
Solution Approach 2:
A liquid reservoir is introduced as an intermediary element between the condensation process and the evaporation process. This intermediary component absorbs excess liquid during overloading conditions and releases it gradually, protecting the plate heat exchangers from damage while maintaining efficient operation.
3Speed
If sub-cooler is positioned above heat exchanger, then gravitational drainage is improved, but oil contamination risk increases
Solution Approach 1:
A liquid reservoir is positioned between the sub-cooler and the evaporator to intercept condensate before it enters the evaporator. This intermediary reservoir allows gravitational drainage to continue while preventing oil-contaminated liquid from reaching the evaporator, thus protecting against oil contamination.
Solution Approach 2:
The system extracts or removes the harmful element (oil-contaminated condensate) from the circulation path by using the liquid reservoir to separate and hold this contaminated liquid, preventing it from re-entering the heat exchangers and causing contamination.
4Device complexity
If single compressive step is used, then system simplicity is improved, but achievable temperature is insufficient
Solution Approach 1:
The auto-cascade refrigeration system enables continuous refrigeration action through a single compressor by utilizing the phase change and heat transfer properties of mixed refrigerants. The system maintains continuous cooling without standby periods by ensuring that condensate from one heat exchanger continuously feeds the next, eliminating idle time and maintaining productive cooling action throughout the cycle.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design allows for faster recovery from defrost and overload conditions, reduced energy consumption, and improved stability, enabling efficient operation without a standby period, with enhanced heat transfer and reduced risk of oil contamination, thus achieving stable temperature control across a wide range.
Implementation Method 1
flow metering devices that create a Venturi effect to enhance heat transfer and stability
Implementation Method 2
a heat exchanger to condense at least some of the fluid
Implementation Method 3
an evaporator to evaporate the fluid into a return or suction stream
Implementation Method 4
a sub-cooler is provided and a flow of condensed liquid refrigerant passes from a high pressure side of the sub cooler to a low pressure side of the sub-cooler
Data Source
Figure 1~2
Figure 3~4
Figure 5~5b
AI summary
The invention describes a method of arranging internal components, their orientation and dimensions within a cascade refrigeration system to increase the system's operating efficiency with respect to energy consumption. The invention also facilitates the early and stable establishment of a multi-stage cascade refrigeration process, and increases its robustness under over-load conditions. The invention also reduces fouling of the heat exchange surfaces and internal functional parts by oil or other contaminants. The invention also provides refrigerants which are of particular benefit when used in the system.